ABSTRACT
PURPOSE: To investigate the hypothesis that positional and anatomic variations during radiation therapy induce changes in lung and heart volumes and associated radiation doses. METHODS AND MATERIALS: In this longitudinal investigation, variations in lung and heart volumes and standard dose parameters of mean lung dose, lung V20Gy, mean heart dose, and heart V40Gy were analyzed on weekly 4-dimensional CT scans of 15 lung cancer patients during conventionally fractionated radiochemotherapy. Tumor, individual lung lobes, and heart were delineated on the mid-ventilation phase of weekly 4-dimensional CT scans. Lung lobes and heart were also contoured on individual breathing phases of pre-, mid-, and end-of-treatment scans. Planning dose was transferred to consecutive scans via rigid registration. Volume and dose variations were assessed relative to the initial planning scan. RESULTS: Interfraction lung volume variability relative to week 0 was twice as large as tidal volume variability (8.0% ± 5.3% vs 4.0% ± 3.3%, P=.003). Interfraction lung volume variation ranged between 0.8% and 17.1% for individual patient means. Lower lung lobes had larger volume variability compared with upper lobes (13.5% ± 8.1% vs 7.0% ± 5.0%, P<.00001). Average mean lung dose variation was 0.5 Gy (range, 0.2-1.0 Gy for individual patient means) and average lung V20Gy variation 0.9% (range, 0.2%-1.6%). Average heart volume variation was 7.2% (range, 3.4%-12.6%). Average mean heart dose variation was 1.2 Gy (range, 0.1-3.0 Gy) and average heart V40Gy variation 1.4% (range, 0%-4.2%). CONCLUSIONS: Anatomic and positional variations during radiation therapy induce changes in radiation doses to lung and heart. Repeated lung and heart dose assessment will provide a better estimate of the actual delivered dose and will improve prediction models for normal tissue toxicity, if assessed in larger cohorts.
Subject(s)
Carcinoma, Non-Small-Cell Lung/radiotherapy , Heart/radiation effects , Lung Neoplasms/radiotherapy , Lung/radiation effects , Organs at Risk/radiation effects , Aged , Carcinoma, Non-Small-Cell Lung/diagnostic imaging , Female , Four-Dimensional Computed Tomography , Heart/anatomy & histology , Heart/diagnostic imaging , Humans , Linear Models , Longitudinal Studies , Lung/anatomy & histology , Lung/diagnostic imaging , Lung Neoplasms/diagnostic imaging , Male , Middle Aged , Organs at Risk/diagnostic imaging , Radiotherapy Dosage , Tidal Volume/radiation effectsABSTRACT
PURPOSE: To determine whether regional ventilation, as measured using 4-dimensional computed tomography (4D-CT), declines after radiation therapy (RT). METHODS AND MATERIALS: We analyzed pretreatment 4D-CT scans associated with 2 RT courses. We quantified regional pulmonary function over equivalent dose in 2 Gy (EQD2α/ß=3) intervals of 0 to 5 Gy, 5 to 20 Gy, 20 to 40 Gy, and >40 Gy using percentile-normalized intensity-based (VentInt) and Jacobian-based (VentJac) ventilation metrics. We modeled the impact of dose on mean ventilation (Vent¯) and regional tidal volume (rTV: tidal volume [TV] within a dose interval normalized to total lung TV). We also identified clinical and dosimetric factors that affected regional ventilation changes (ΔVent¯ and ΔrTV) after RT for the >20 Gy dose interval. RESULTS: After RT, Vent¯Int exhibited statistically significant dose-dependent declines within the 20 to 40 Gy (-5.0%; P=.03) and >40 Gy (-6.8%; P<.01) intervals. Vent¯Jac exhibited a declining trend after RT only for the >40 Gy interval (-4.6%; P=.07). Factors associated with ΔVent¯Int for the >20 Gy dose interval included airway stenosis progression (P=.03) and gross tumor volume (P=.09). Both rTVInt and rTVJac were associated with small (<2%) but significant declines after RT for 20 to 40 Gy and >40 Gy intervals. Factors associated with declining rTVInt (P<.05) for the >20 Gy dose interval included airway stenosis progression, greater V20 (volume of lung receiving >20 Gy), and smaller fraction of emphysema in V20. The association between the absence of chronic obstructive pulmonary disease and declining rTV trended toward significance (P=.09). CONCLUSIONS: Regional ventilation, as measured using 4D-CT, demonstrates a dose-dependent decline after RT. Our results support the use of 4D-CT ventilation imaging for monitoring regional pulmonary function change after RT.
Subject(s)
Four-Dimensional Computed Tomography , Lung Neoplasms/diagnostic imaging , Lung Neoplasms/radiotherapy , Lung/diagnostic imaging , Lung/radiation effects , Respiration/radiation effects , Aged , Female , Humans , Lung Neoplasms/physiopathology , Male , Pulmonary Disease, Chronic Obstructive , Radiation Pneumonitis/diagnostic imaging , Radiotherapy Dosage , Regression Analysis , Retrospective Studies , Statistics, Nonparametric , Tidal Volume/physiology , Tidal Volume/radiation effectsABSTRACT
Resumo: A irradiaçäo dos campos tangentes mamários inclui certa quantidade do volume pulmonar, o que pode levar a uma pneumonite radiógena. O volume de pulmäo irradiado pode ser avaliado medindo-se a altura do parênquima pulmonar irradiado (API) pelas radiografias de posicionamento ("portals"). Considera-se tecnicamente satisfeitos sempre que a API for menor ou igual a 2,5cm. Analisamos retrospectivamente "portals" de 100 pacientes, tratadas entre janeiro de 1996 e junho de 1997. Tomamos o contornodas mamas das pacientes e, por intermédio da geometria do feixe de radiaçäo, observamos o ângulo para incidência dos campos tangentes . Em 71 por cento dos casos este ângulo conduziu a uma API maior do que 2,5cm o que necessitou novo arranjo dos campos. Realizamos análise estatística objetivando encontrar uma expressäo matemática que relacionasse a API com os parâmetros geométricos do tratamento. O ajuste linear obtido, embora útil, näo foi inteiramente satisfatório, provavelmente devido a variaçöes anatômicas individuais ou a exclusäo de variáveis.
